A π-conjugated conductive polymer, which is composed of a conjugated system having a main chain containing π-electrons, can be synthesized by an electrolytic polymerization method and a chemical oxidation polymerization method.
In the electrolytic polymerization method, a π-conjugated conductive polymer on a substrate is formed into a film by dipping a substrate, such as a preformed electrode material, into a mixed solution of an electrolyte as a dopant and a precursor monomer for forming a π-conjugated conductive polymer. Therefore, it was difficult to manufacture a π-conjugated conductive polymer in large quantities.
On the other hand, in the chemical oxidation polymerization method, there are no restrictions such as those in the electrolytic polymerization method, and it is possible to manufacture a large amount of a π-conjugated conductive polymer in the solution by adding an oxidizing agent and an oxidation polymerization catalyst to a precursor monomer of a π-conjugated conductive polymer.
However, in the chemical oxidation polymerization method, since the solubility of a π-conjugated conductive polymer in a solvent becomes poor with the growth of a conjugated system of the main chain of the π-conjugated conductive polymer, insoluble solid powder is obtained. It is difficult to uniformly form a π-conjugated conductive polymer film on the surface of a substrate using an insoluble solid powder.
Therefore, a method of solubilizing a π-conjugated conductive polymer by the introduction of a functional group, a method of solubilizing a π-conjugated conductive polymer by the dispersion in a binder, and a method of solubilizing a π-conjugated conductive polymer by the addition of polyanions have been proposed.
For example, in order to improve the dispersibility in water, a method has been proposed of manufacturing an aqueous poly(3,4-dialkoxythiophene) dispersion by the chemical oxidation polymerization of 3,4-dialkoxythiophene using an oxidizing agent under the presence of polystyrene sulfonic acid, which is a polyanion having a molecular weight in a range of 2,000 to 500,000 (refer to PTL 1). Further, a method has been proposed of manufacturing an aqueous π-conjugated conductive polymer colloid dispersion by chemical oxidation polymerization under the presence of polyacrylic acid (refer to PTL 2).